In machining, boring, milling, and similar operations involving metal, wood, plastics, ceramics, composites, and other workable materials, it is generally difficult to determine the overall health and efficiency of the material removal process. Methods most often employed by the machinist include visual inspection or the sound of the operation. This is generally a very subjective assessment invariably based on the experience of the individual machinist.
U.S. Pat. No. 4,978,909 to Hendrix et al. describes a demodulation circuit for motor current spectral analysis. Motor current is monitored, filtered, demodulated and amplified, and then fed to a frequency analyzer for determination of motor current signatures. In this Patent, the peak frequencies are analyzed and correlated to certain operating parameters.
U.S. Pat. No. 5,058,434 to Zaschel discloses a process for early detection of damage to machine parts. The process involves the use of transducers to sense machine vibration. The transducers produce an electrical signal which is broken down into periodically determined stochastic components.
U.S. Pat. No. 3,842,663 to Harting et al. discloses an apparatus for detecting defects in a mechanical system, in which a transducer is used to produce an electrical signal. The signal is demodulated and then spectrally analyzed.
U.S. Pat. No. 5,187,434 to Ando discloses an apparatus for detecting machining conditions of a workpiece. Excitation current to a magnetic bearing is monitored and compared to preset values to derive a machine condition.
U.S. Pat. No. 4,965,513 to Haynes et al. discloses a motor current signature analysis technique in which current peaks at specific frequencies are analyzed to determine operability of a valve.
Certain types of machine operating parameters would be difficult to analyze using prior art techniques. For example, the gradual wear of a cutting tool would not necessarily produce an observable frequency phenomenon. Thus, a continuing need exists for current signature analysis techniques which are not dependent on discrete frequency analysis.